This invention relates to electronic voltage and current regulators and more particularly to a control device for a circuit arrangement whereby an inductive load is fed by a direct current source through a semiconductor regulator which contains two parallel, switching, controllable semiconductor rectifier elements with identical current conductions and within the control circuit is an arrangement for the generation of clock frequency signals.
In addition to semiconductor rectifier elements and the clock frequency signals, there is an inductive impedance in the circuit, connected to and on the output side of each semiconductor rectifier element. The input side connection point of each semiconductor rectifier element is connected to a terminal of the direct current source. Moreover, the center tap connection point of the inductive impedance is connected to a terminal of the load. The output connection point of the semiconductor rectifier element is connected to the input of the inductive impedance and to a discharge diode, the other end of this diode being connected to the other terminal of the load. The inputs of the semiconductor rectifier elements are connected to the control circuit, which generates two clock frequency signals electrically offset from each other by 180 degrees. These signals are each fed by means of a control circuit to the semiconductor rectifier elements in such a way that they are alternately non-conducting and conducting in an 180 degree offset pattern.
A control circuit of this type is described in U.S. Pat. No. 4,417,197. Transistors or thyristors make up the semiconductor rectifier elements. The inductive impedance, which is switched in series with the controllable semiconductor rectifier element constitutes a low-pass filter, together with a filter capacitor which in turn is in parallel with the load impedance. The non-interconnected inductive impedances provide a delayed current rise and fall in order to reduce the ripple current originated by the timing as much as possible. At the capacitor and therefore at the load impedance, there is a relative higher voltage than at the input side of the semiconductor rectifier element. Thereby the voltage at the capacitor and at the load impedance has ripple current with a frequency twice as high as the timing pulse frequency. The switching noises of the semiconductor elements have been reduced because the semiconductor rectifier elements of the frequency converter only need to be driven at half the timing clock frequency as compared to other chopper switches. The circuitry described in U.S. Pat. No. 4,417,197 is, however, not suited for the feeding of individual inductive loads, such as motors. With such loads, there is a strong possibility of an actual noise increase at the load.
A direct current converter is described in the British publication GB-A-No. 1 007 169. In the case of this converter, a load is fed by a direct current source through a semiconductor controller containing two parallel switching controllable semiconductor rectifier elements of identical conductance direction. It has an arrangement used to generate clock frequency signals in such a way that the semiconductor rectifier elements are non-conducting and conducting alternately and offset by 180 degrees. The semiconductor rectifier elements are switched on the output side of an autotransformer with a center tap point whereby the input connection point of the semiconductor rectifier elements is connected to a terminal of the direct current source and where the center tap point is connected to a terminal of a load impedance. The connection points of the semiconductor rectifier elements with the autotransformer are connected through a diode to the other terminal of the load. In this arrangement, the load is embodied by an resistive load, as this is the case in, for example, electronic switching systems, remote control systems or computers. The semiconductor rectifier elements are made of transistors whose control voltages are taken from windings coupled to the autotransformer. In this case both transistors are non-conducting and conducting alternately and offset by 180 degrees so that one obtains at the load a direct current composed of half wave voltage pulses or blocks sequentially added in time. The resulting direct current voltage occurring at the load has half the value of the battery voltage put on the autotransformer, and it is not without discontinuities. The autotransformer of the known direct current converter also acts as a symmetrical voltage divider for the battery current. A control of the voltage, or of the current put onto the load has not been arranged. With this known direct current converter it is not possible, however, to control the power output of an inductive or resistive load.
Parallel switches made of transistors are known from British publication GB-A-No. 1 371 418. In their case one will encounter measures for the obtaining of an identical active current in each transistor by means of coupling transformers. A drive system controlled by a micro processor where a direct current motor is controlled from a battery through a transistor, is known from the article in the publication IEEE Transactions on Industry, volume 1A-17, number 6, November / December 1981, pages 626 through 631. This article shows a direct current motor switched in parallel with a discharge diode. In order to drive the direct current motor as a power generating brake, an additional transistor with an additional discharge diode has been included.
It is an object of this invention to provide a controlled circuit in which the ripple current supplied to the load of a variable-power, small inductive load is further reduced. Another object of the invention is to effectively reduce the noise which occurs at the load because of the current pulsing.